Edward Donnerstein, Daniel Linz, Steven Penrod, The Question of Pornography: Research Findings and Policy Implications, (1987), The Free Press - A Division of MacMillan, Inc., Chap. 3, p. 70.
One part of this study is sometimes misinterpreted. When referencing this study, some articles note that during the pre-teen years (a category not covered in the above source, but mentioned in the Goldstein and Kant source cited below), the rapists saw more explicit porn compared to a non-offender control group. This is true only for the rapists vs. ONE of the control groups. Two other control groups were used, and one of these other control groups saw more of the explicit porn during the pre-teen years than did the rapists.
See Michael Goldstein and Harold Kant (with John Hartman), Pornography and Sexual Deviance (1973), University of California Press, p. 55-58, 183.